1. Field of the Invention
The present invention relates to a display unit in a remote display system performing a long distance transmission of an analog video signal.
2. Description of the Background Art
In a display system where a video sending device and a display unit are displaced at relatively distant places from each other, when an analog video signal is transmitted over long distances without high-frequency modulation, it is transmitted as a differential analog video signal, using a balanced line for a long distance transmission line in order to enhance resistance to disturbance noise.
The differential analog video signal can be transmitted with a much wider band when transmitted as baseband signals rather when than being subjected to high-frequency modulation. However, there is influence of frequency response characteristics of the aforementioned long distance transmission line and a transmission drive circuit, so that it is necessary to adjust on the basis of correction parameters using a correction circuit of the frequency response characteristics. Further, differences of propagation delay of a line transmitting a plurality of signals such as the red, green, and blue signals cannot be ignored, so that it is necessary to adjust on the basis of the correction parameters using a correction circuit of the aforementioned propagation delay.
If the image quality is such that propagation delay for each frequency and distortion for each linear characteristics level of a drive circuit cannot be ignored, it is necessary to form and add a correction circuit for each strictly, but causing a circuit to be expensive. Therefore, in the present specification, a technology will be described as applied to a display unit at a level to be allowable by absorbing the deterioration of the image quality with adjustment of the aforementioned propagation delay correction.
Conventionally, as an example of disposing a plurality of display units in a display system, video signals are distributed to each of the plurality of display units by providing a diverging device of long distance video signals outside of each of the display units, as an intercom system disclosed in Japanese Patent Application Laid-Open No. 2006-304219 (paragraphs [0018] to [0056], and FIG. 1).
Further, for example, U.S. Patent Application Publication Nos. 2006/0119594 (paragraphs [0002] to [0106], and FIG. 1), and 2008/0186407 (paragraphs [0016] to [0056], and FIGS. 4 to 6) disclose a configuration of distributing video signals with a long distance video transmission line and disposing a receiving device outside the display unit.
The conventional display unit disclosed in the documents such as Japanese Patent Application Laid-Open No, 2006-304219 in the above is generally configured to provide a receiver (receiving device) outside the display unit, as described above. This has caused the following problems (1) to (3).
(1) In accordance with a device layout, a long cable for connecting an external receiver and a display unit, a strong amplifier, and an external electromagnetic noise countermeasure circuit are needed for each of power source, a video signal, and a control signal.
(2) In system installation sites, operation cost is produced accompanying a wiring operation of cables including an operation of screwing cables such as a VGA cable, a RS-232C cable, and the like.
(3) In setting parameters in a receiver, when a result obtained by automatically adjusting with the receiver itself is fine adjusted manually, an adjusting switch of the receiver itself is to be used. Also, when it is adjusted and controlled from both sides of a host computer and a remote controller of the display unit, a switching device for an adjustment and control host is needed to be provided in the receiver itself.
Furthermore, the conventional display unit disclosed in the documents such as U.S. Patent Application Publication Nos. 2006/0119594 and 2008/0186407 has a configuration of providing a distributor so as to be independent from the receiver outside the display unit. This needs an external wiring as a plurality of long distance transmission signal lines, and causes a problem that operation cost is produced accompanying a wiring operation of cables.